I need to rant. My fiancé's best friend was engaged. The girl who he was engaged cheated on him…

I need to rant. My fiancé's best friend was engaged. The girl who he was engaged cheated on him pretty much their entire relationship. When he found out he broke off the engagement. I guess they have been talking again and got officially back together. I don't trust her or like her. I hate to see them together because of her my fiancé and his best friend barley ever hangout anymore